feat: add OpenCode 2 command loop actions

[ByBrawe]

Summary

• add experimental OpenCode 2 command-action support for ordinary slash commands such as /review --quick
• detect real session.command and session.shell capabilities separately; prompt-only hosts remain valid, while command loops are rejected with command-capability if command transport is unavailable
• keep shell actions unsupported because the real @opencode-ai/plugin@next context currently exposes session.command but not session.shell
• extend the V2 host contract and runtime adapter with normalized command transport using the verified { sessionID, id, arguments, ...optional } request shape; undefined optional fields are omitted before the real host call
• wire command transport into the experimental plugin only when the host capability is present
• generalize the idle-safe prompt scheduler to dispatch both prompt and command jobs with the same interval/max-runs/state-persist-before-transport semantics
• keep /compact outside command transport because the shared V1 actionKind() treats it as the dedicated compact action before forced-command classification
• add direct command runtime tests, adapter/composition tests, host-contract tests, and capability sentinel coverage
• strengthen the V2 Lifecycle Contract so the new command tests run on Ubuntu and Windows
• strengthen the real OpenCode 2 adapter gate to require sessionCommand=true from the actual @opencode-ai/plugin@next context while recording the available session method surface

Branch validation passed syntax, host contract, capability sentinel, and command runtime tests. During validation, two test/wiring issues were caught and fixed: a prompt-only subscribe fixture used the wrong event-subscription shape, and adapter requests carried undefined optional fields. The official PR gates now cover the corrected exact head. Temporary capability-probe workflow was removed before this PR. Package version remains 0.5.28.

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